Many natural waters and industrial contaminated waters have elevated concentrations of metals, metalloids, and other contaminants that may present threats to human health and the environment. For example, flue gas desulphurization (FGD) contaminated water, a byproduct of a process to remove sulfur dioxide from exhaust gases from coal fired power plant operations, usually includes high concentrations of contaminants, such as arsenic (As), mercury (Hg), selenium (Se), perchlorate (ClO4−), and nitrate (NO3—N) which must be removed prior to being discharged back into the environment and/or water supply. Agricultural drainage may also contain high concentrations of Se, NO3, As, and other contaminants. Drainage from surface and underground mining operations, including coal mines, non-ferrous metal mines and iron ore mines may also be acidic or basic, and/or may include high concentrations of metals and/or metalloids including As, antimony (Sb), barium (Ba), beryllium (Be), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), Hg, nickel (Ni), (Se), technetium (Tc), Thallium (Tl) uranium (U), vanadium (V), and/or zinc (Zn).
In addition to the metals, metalloids, and nitrates listed above, contaminated waters from these and other industrial operations frequently contain high concentrations of total dissolved solids (TDS), non-regulated cations such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), and non-regulated anions, such as chlorides (Cl), bicarbonates and carbonates (HCO3−/CO32−), perchlorates (ClO4−), sulfates (SO42−), and silica (SiO2). The presence of high TDS and non-regulated constituents makes removal of the regulated constituents very difficult.
Today's methods of treating contaminated water contaminated with metals, metalloids, and other contaminants rely heavily on physical and chemical processes. Chemical precipitation can be used to remove many metals but is generally not effective for removing metalloids (e.g., As and/or Se) and/or metals that form oxyanions, such as, for example, chromate (e.g., CrO42−), molybdate (e.g., MoO4−), or uranyl dicarbonate (e.g., UO2(CO3)22−).
Current methods based on adsorption onto iron oxides can remove some metalloids (e.g., As) but not others (e.g., Se) from contaminated water. Ion exchange can remove most metals, metalloids and/or other contaminants, but selective removal of such metals, metalloids, and/or contaminants is not effective for treating contaminated waters with very high TDS concentrations. Membrane processes such as reverse osmosis (RO) or electrodialysis reversal (EDR) are desalination processes that will remove all dissolved constituents but are expensive and difficult to operate, remove virtually all dissolved constituents resulting in production of large volumes of waste that are difficult to manage, and/or recover only a fraction of the feed water thereby resulting in a large loss of water which may be valuable. Other than desalination methods, there is no technology which can simultaneously remove all of the regulated metals and metalloids in a single process.
Known biologically-based technologies for treating water are based on growth of microorganisms that are attached as a biofilm grown to a solid surface (hereinafter sometimes referred to “solid substrate”), such as particles of sand, granular activated carbon (GAC), plastic beads or sheets (hereinafter, “attached growth technology,” “conventional reactor,” and/or “substrate based technology). For example, one such attached growth technology includes attached growth organisms that are grown on GAC in a column configuration in which metals, metalloids, and/or other contaminants (e.g., nitrates, sulfates, etc.) are reduced by a population of anaerobic bacteria (hereinafter referred to as “anaerobes” or “anaerobic bacteria”) that attach to the surface to form a bacterial layer (sometimes referred to as a “slime layer”). The anaerobic bacteria can reduce the dissolved metals, metalloids, and/or other contaminants within the contaminated water with subsequent formation of a precipitate, which can be removed by filtration. Another attached growth technology includes an up-flow fluidized bed reactor in which a film of anaerobic bacteria attached to the surface of a granular media reduce the metal, metalloids, and/or other contaminants within the water to form a precipitate.
Unfortunately, the bacterial layer that is formed in attached growth technologies is fragile and can sometimes be destroyed, reduced, or damaged by processes such as abrasion or toxic constituents. Additionally, the bacterial population that is attached to the physical substrate may be associated with long and/or multi-stage treatment cycles and/or large volumes of support media (e.g., tanks, agitators, plumbing, etc.) to maximize the surface area of the physical substrates. Finally, it is difficult to maintain a concentration of bacteria, associated with an attached growth technology, to ensure that a biological reaction rate, of the bacterial layer, is sustained and/or long detention times for removal of metals, metalloids and other non-metal contaminants are avoided.